Mineralogy and Petrology Notes
Go over syllabus
Review rock cycle, types of rocks, how they each form and the story that they tell.
Play game: Name that rock or mineral
1 point for each mineral identified, 1 point for composition
1 point for each rock identified, 1 point for story it tells.
Physical Properties of Minerals
Crystal faces: faces are planes in the crystal with particular ion/atom densities and arrangements.
Faces reflect underlying symmetry of the crystal
Habit: Malformations, differential growth rates, restrictions of growth area
euhedral
subhedral
anhedral
Luster, color, streak
luster: way light reflected, refracted, metallic and nonmetallic: vitreous (Qz), resinous (sphalerite), pearly (talc), greasy silky (milky qz), adamantine (refractive index)
color: a few are diagnostic (azurite, malachite, turquoise), some vary according to exposure to air (bornite), some by trace composition (Quartz, sapphire, ruby), some by major composition (pyroxene-talk about effect of amount and color)
streak: color of powder, especially useful for oxides. E.g. hematite always has red streak, but color not always red.
translucency: metallic oxides often opaque, most silicates, carbonates, sulfates, others are transparent or translucent if sliced thin enough.
Cleavage, parting, fracture
Planes of weakness in the crystal,
parting is breaking along other planes of weakness, such as twinning surface, exsolution surface.
fracture-no planes of relative weakness (Qz)
break along planes with weaker bonds, e.g. Van der Waals bonding in graphite, easily cleaves along that plane.
Hardness
Mohs scale
Related to bond strength. Different bonds in different directions, so hardness may depend on direction (kyanite), or which crystal face (calcite)
In general, in increasing bond strength/hardness
Van der Waals, hydrogen bonds, ionic bonds, covalent bonds
Tenacity
brittle, malleable, sectile, ductile
Specific gravity
depends on how closely packed atoms are and atomic mass of atoms. (compare to mass= like dividing by mass of H2O, makes dimensionless, but because water has a density of 1g/cc, you get the same number)
Magnetism (diamagnetic and paramagnetic and ferromagnetic)
radioactivity, solubility in HCl
Piezoelectric
non-conductor, otherwise it shorts itself out. Must not have center of asymmetry (that is, its atomic arrangement is different in one direction from the other along some axis, or polar). Used in altimeters, pressure gauges, timer in watches and computers. Hydroxyapatite is piezoelectric, important in bone formation.
Reactions, Stability, and Behavior:
Crystallization:
Concept of phases: phases are macroscopically homogeneous regions bounded by distinct edges.
gases, liquids, solids are the examples of phases you learn in high school. But a particular material can exist in more than one solid or liquid phase. For example, graphite and diamond are two solid phases with the same composition (polymorphs).
In gases, individual molecules or atoms have no long range order, and are not bonded to nearby molecules or atoms.
In liquids, molecules or atoms have no long range order but are bonded to nearby molecules or atoms but those bonds are not strong enough or persistent enough to maintain a regular long-range order, although a short-range order often exists.
In solids, molecules and atoms are bonded to nearby modecules and atoms, most normally establishing both local and long range order (crystals). Some solid materials do not have long range order (although short range order typically exists). These amorphous materials are called glass.
Crystallization occurs when a material goes from a gaseous or liquid state to a solid, ordered state. This occurs when T, P, composition or other properties change in such a way that the solid state is energetically favored over the former state.
For example, evaporating water from salt water increases the concentration of Na and Cl dissolved in the water to the point that salt crystals will form.
Cooling magma will bring the temperature to a value where crystals begin to form in the melt.
Phase Diagrams, graphical illustration of crystallization reactions and phase transitions.
One-component reactions (different phases of a single chemical component)
Primary variables are T and P.
In general, the phase preferred at higher pressure will be the denser phase.
The phase preferred at higher temperature will be the less well-ordered phase and/or the phase with higher energy bonding.
Water on blackboard: Phase diagrams illustrate fields of T and P where phases are stable. Lines represent reactions, such as the reaction in which liquid water freezes to ice (find that reaction).
Water-salt binary on blackboard, basic ideas of composition change, number of phases, degrees of freedom,
The six crystal systems in 3-D
(from least to most symmetry)
show lack of symmetry with parallelogram in 2-D (although point out rotation axis).
Classification of Minerals:
Crystal structure and symmetry are not the only important characteristics of a mineral. Chemical composition is also important. Minerals are often classified into mineral groups.
Mineral groups are based on the primary anion (not cation) of the crystal. This is because minerals with a common cation usually have more in common in terms of properties than do minerals with common cations (for example, compare cerrusite and siderite to galena and pyrite). Also, the anion more consistently reflects the geological environment of formation. That is, sulfides tend to occur together in one type of environment, whereas carbonates occur together in a different environment, and silicates in a third environment.
Native elements (metals and nonmetals) (no anion)
e.g. Cu, Au, Fe, Fe-Ni
e.g. S, C
bonds are metallic in metals, or covalent or other in nonmetals
Sulfides (and sulfarsenides, aresenides, antimonides, selenides, and tellurides) (S, As, Sb, Se and Tl are anions)
e.g. FeS2 (pyrite or marcasite), ZnS (sphalerite or wurtzite), arsenopyrite (FeAsS - arsenic substitutes for S), CuS (covellite), Cu2S (Chalcocite), Cu5FeS4 (bornite).
bonds are mainly ionic, although there are also covalent bonds and metallic bonds.
Usually opaque with distinctive streaks and colors
Oxides (and hydroxides)
e.g. Fe2O3 (hematite), Al2O3 (corundum), Ilmenite (FeTiO3), Magnetite (Fe3O4), cassiterite (SnO2), goethite (FeO(OH)).
bonds are mostly very strong ionic bonds. These minerals are often very hard. Oxides are usually very stable minerals.
Oxides are important ore minerals, including Fe, Cr, Mn, U, Sn, Al (although the stability means that substantial energy investment must be made to separate the metal from the oxygen). Ruby and Sapphire are members of this group.
Halides
The halides include F, Cl, Br, I, etc. e.g. NaCl (halite), KCl (sylvite), CaF2 (fluorite)
Bonding is the most completely ionic of any of the mineral groups because the electronegativities of the constituent elements are the most different.
This group has the highest crystal symmetries because ions are spherical and bonds are symmetrical. Symmetry decreases as cations of higher valence than 1 are involved, and the bonds become more covalent.
Have the characteristics of ionic solids: e.g. low hardness, poor conductors
Carbonates: (and nitrates)
e.g. CaCO3 (calcite, aragonite), FeCO3 (siderite), CaMg(CO3)2 (dolomite), Cu2CO3(OH)2 (malachite), Cu2(CO3)2(OH)2 (Azurite).
Triangular anionic complexes bound more strongly than the complexes are bound to other ions. Each oxygen has a residual charge of -2/3. Bonding of the CO3 group is not as strong as CO2 bond, so in presence of H+, the carbonate group becomes unstable, breaking down to form CO2 and water.
Bonds in the complex are covalent, bonds between complex and metal cations are ionic.
Calcite structure: Like halite, but with CO3 groups in place of Cl and Ca in place of Na. Symmetry of the triangular CO3 groups produces a rhombohedral rather than isometric crystal.
Sulfates:
e.g. BaSO4 (Barite), CaSO4 (Anhydrite), CaSO4۰2H2O (Gypsum).
non-polymerizing complexes.
Nitrates, Borates, chromates, tungstates, molybdates, phosphates, arsenates, vanadates.
anionic complexes bound more strongly than the complexes are bound to other ions.
Silicates:
Key idea: whether and how the silica tetrahedra are connected to each other by strong covalent bonding, or whether the corners of tetrahedra connect to octahedral or other sites occupied by usually-larger cations by ionic bonds.
Nesosilicates: olivine
remind of model that we looked at. Show overhead. Point out that tetrahedra share corners with octahedra (M1 and M2), not other tetrahedra. no O shared, share in 0 dimensions. review olivine SS series.
Inosilicates: Single Chain Silicates: The pyroxenes.
share in 1 dimension
Draw single chain on board (2 of 4 O shared, 1:3):
Review SS series for The clinopyroxenes (monoclinic) and orthopyroxenes (orthorhombic):
Draw illustration:
Phyllosilicates (sheet silicates)
Structure of micas:
Similar to the structure of illite looked at in lab (triangles represent tetrahedra in 2-D, diamonds represent octahedra in 2-D).
Muscovite KAl2(AlSi3O10)(OH)2 - K between covalent octahedra-tetrahedra sandwiches, OH substituting for some O in octahedra, Al in octahedra, other Al substituting for Si in tetrahedra. Dioctahedral because Al is trivalent, not all octahedral sites are occupied (2 of 3). Is the Si-O ratio correct? Have to compensate for the Al on the tetrahedral sites. So better to think of the T-O ratio.
Also, consider substituting Mg, Fe for Al (Phlogopite, biotite)
Tectosilicates: share in 3-D (all 4 O shared with another tetrahedron): Draw picture. Show substitution of Al, charge balance with Na, lead into Albite, then plagioclase SS series review. Talk about Al-Si substitution and solid solution at length.
Common Rock forming minerals:
Olivine (solid solution)
Pyroxene (solid solution, miscibility gap between ortho and clino)
Amphiboles
Feldspars (plagioclase series and orthoclase)
Feldspathoids (nepheline)
Micas (muscovite, biotite)
Quartz
Clay minerals (smectites, montmorillinites)
Garnet
Kyanite
Petrology, Lab #1 Rock Scavanger Hunt
Get into teams of 2 or 3 people. Each team will get one point for each rock correctly collected.
Find each of the following rocks.
1) A rock that tells the story of being deposited on a beach
2) A rock that tells the story of having formed deep under a mountain range
3) A rock that tells the story of having been formed in a swamp
4) A rock that tells the story of having erupted from a volcano.
5) A rock that tells the story of having formed in a salty, arid sea
6) A rock that tells the story of having formed in a fast flowing river
7) A rock that tells the story of having cooled slowly deep in the Earth's crust.
8) A rock that tells the story of cooling slowly in the crust for a while, then erupting.
9) A rock that tells the story of forming under a mountain range, but not as deep as (2)
10) A rock that tells the story of forming in a subducting lithospheric plate
11) A rock that tells the story of forming in a continental rift
12) A rock that tells the story of forming in a volcanic arc at a subduction zone
13) A rock that tells the story of forming near an igneous intrusion
14) A rock that formed in an alluvial fan on the flanks of a mountain range.
15) A rock that tells the story of forming in an oxygen-poor ocean
16) A rock that formed where crystals settled at the bottom of a large magma chamber
17) A rock that formed on a continental shelf, abundant in life but with little sand or mud from land
After confirming which rocks are "right", return them to their correct locations.
Petrology, Lab #2 Review of Rock-forming minerals
Have them get into teams of 2 or 3 people. Identify minerals (if more than one mineral, identify them all!)
After sufficient time (a waited 90 minutes but those who finished well before this were getting tired by end-took about 25-30 minutes to go through them), go through the minerals with them, talking about key characteristics. They score their own labs before handing in.
M11- 3 minerals, pyroxene, phlogopite, Quartz, also is a feldspar or andalucite or something, not sure.
M16-calcite rhombohedral crystals
M3 fluorite
M7 garnet (andradite) and dolomite (Ca3Fe2Si3O12)
Siderite
Perthite
M9-Biotite and Na-spar
Samples from MN: hematite, and jaspar
pegmatite: tourmaline, Na-spar, quartz, k-spar
granite with polished side: K-spar, Na-spar, qz, biotite, hornblende (what say about P? Crystallization sequence?)
158 fluorite with calcite
13 hornblende syenite (K-spar, perthite or Na-spar)
87 garnet (Fe3Al2Si3O12) (pyrope ss) and silliminite
215- amethyst (how distinguish from fluorite?)
35A dolomite (how distinguish from calcite?)
46A Chalcedony
10ab pyrite (with striations and cubes)
46E1436 Calcite cleavage rhomb
m1 alabaster gypsum
m2 selenite gypsum
46E4887 specular hematite
m13 pyrite
sphalerite
Petrology
Sedimentary Petrology
Terms related to deposition
Detrital = transported fragments and particles
Clastic = fragments and particles that may not have been transported.
Chemical and biochemical = precipitated from water
Major rock types
Sandstone (20-25%): clastic rock with particles 0.06 to 2mm.
Mudstone (65% of sedimentary): clastic rock with particles less than 0.062mm
Carbonate (10-15%): usually chemical or biochemical rock made of carbonate minerals, particularly calcite, aragonite, dolomite and some siderite and magnesite.
Evaporites: Chemical rock, usually formed from evaporation of sea water, or terrestrial alkaline or salty waters, in arid, restricted basins.
First three make up >95% of sedimentary rocks.
Problems in classification:
A carbonate might be made of clastic fragments (either transported or not), such as large fossil fragments in a limestone, or wave-worked shell fragments in a coquina.
Variable amounts of clastic clay can mix with carbonate (Marl).
Age distribution of sedimentary rocks
Half of sedimentary rocks are 130myo or younger (Cretaceous or younger).
Exponential decline in exposure as go to progressively older rocks.
Does that mean that sedimentary rocks form more commonly today than in the past?
No, is related to a roughly constant probability of destruction by erosion, with a certain fraction of older rocks surviving to later time periods.
Common depositional settings
Most sedimentary rocks are deposited in marine (as opposed to terrestrial) environments. This is because oceans constitute a larger fraction of earth’s surface, because marine environments are more likely to be depositional rather than erosional, and because the sediments are more likely to be covered by later sediments rather than eroded.
Due to fluctuations in sea level, shallow marine water invading continental areas has been more pervasive at various times in the past than they are today. These shallow seas are called epicontinental seas.
Depositional Basins (regions either significantly below base level, or where persistent subsidence provides room for deposition over extended time periods.)
activity: in groups, try to identify key plate-tectonic environments, and the general characteristics of sediments deposited in each.
Oceanic Basins: deposits underlain by oceanic crust (basaltic rather than granitic)
a few key considerations: water depth affects light penetration, fossil materials are often pelagic. Deeper, colder water is more acidic, there is a depth below which carbonates are not stable and an even greater depth below which settling carbonates do not accumulate.
Arc-trench system basins: complex system of basins related plate covergence and subduction.
a few key considerations: extensive tectonism and metamorphism makes these regions complex. Often associated with volcanic input. Basins range from extremely deep to not so deep, and may have either oceanic or continental material base. Sediments include mélanges and turbidites, to more fluvial, deltaic, marine as get closer to the continent.
Continental collision basins: basins that develop where continents converge
a few key considerations: include elements of ocean basins prior to convergence, such as ophiolite, and deposits related to the orogeny such as flysch (synorogenic clastic wedge with marine) and molasse (synorogenic clastic wedge-terrestrial-e.g west of appalachians or east of rockies) deposits.
Basins in displaced terrains (exotic or “suspect” terrain):
Key considerations: are tacked onto the edge of a continent by plate movements and so have structural, stratigraphic, and paleontological discordances with the rest of the continent.
Divergent Grabbens: basins that develop during continental divergence
Key considerations: are often on presently-stable continental margins where past divergence of oceanic-basin-formation occurred. volcanics, intrusives common, interbedded with arkosic red beds. In arid climates, evaporates occur.
Intracratonic basins (regions of subsidence in the interior of stable continents)
Key consideration: Deposited in epicontinental seas (non-orogenic, shallow water), with very thick sediments grading laterally into much thinner sediments of similar type. (e.g. Williston Basin, Michigan Basin).
Soils
Horizons:
A (zone of leaching (more extensive leaching in humid), organic accumulation
B (Zone of accumulation (more soluble accumulates in drier)
C (bedrock is altered
Bedrock
Soil formation is a combination of chemical processes weathering rock and minerals and activity of living organisms (technically, only called soil if it is affected by living things, thus the lunar "soil" is more appropriately called a regolith).
Key factors:
Water, and leaching vs evaporation
acidity (pH)
oxygen (Eh)
chelating agents (organic molecules that latch onto metal cations and make them soluble)
Solubility in water: ionic compounds more soluble e.g. Na and Cl, Ca and Fl, K, Mn2+, Fe2+. B3+, P5+, S6+, and C4+ are soluble as oxide anions (e.g. CO32-, PO43-). Covalent bonded compounds are less soluble (e.g. Fe3+, Al3+, Mn4+, Si4+, Mg2+), often insoluble as oxides or hydroxides.
Acidity affected by several factors, including:
abundance of CO2 from plant and animal life, producing carbonic acid,
organic acides
Roots exchange H+ ions for nutrient cations in soil (method of uptake), increasing soil acidity